Getting results
How fast-turnaround DNA analysis became an effective way to catch offenders.
Former detective inspector John Manning reckons he’s solved more serious crimes since he retired in 2005 than he did in more than 30 years in the force. Manning is the national ESR liaison adviser and police go-to person for advice on problematic DNA matters, cold cases and historical sexual assaults. With advances in DNA technology in the mid-2000s, Manning launched a project to re-examine stored exhibits from serious sex crimes between 1990 and 2000. The ESR had retained samples in 47 cases, and when they were reworked, 35 provided a meaningful profile. Of those, 20 linked to men who were already on the ESR’s databank, resulting in charges being laid and eight convictions. Twelve cases could not be progressed. The other 15 profiles, which didn’t match any known offenders or suspects, have now been loaded onto the crime-scene database and can be matched if the same men reoffend.
Manning says police try to target offenders and suspects from whom they expect the “biggest return”. “We want to get the young, active, high-volume offenders on the databank, because we know they’re the people who are likely to leave DNA at a crime scene in the future. There’s no point getting it from an 80-year-old grandma who does a bit of shoplifting.”
Manning was involved in the hunt for Auckland serial rapist Joseph Thompson in the mid-90s, when there was no law to compel a suspect to give a sample. “We had profiles from maybe half a dozen cases and knew we were looking for a serial offender. Joe was on our priority list, anyway [because of his criminal history and where he lived], and he was asked for a sample, but he kept putting it off. Finally, he agreed to provide a buccal [cheek] swab – he said he couldn’t give blood because he was a Jehovah’s Witness.”
About a dozen buccal swabs had been submitted to the ESR in the case before then, but none yielded a profile police could use. Although Thompson’s sample showed promising results early in the analysis, in those days it took three months to develop a full profile.
“Today, we can get one in 48 hours – that’s what we were fighting with. We thought the forensic science was wonderful, but in hindsight, it was bloody slow and cumbersome and slowed things down a lot.”
Police put Thompson under 24-hour surveillance while they waited for the results. “We had an ex-army officer in the police and he used to harness himself up a bloody tree, bring a sandwich and hang in there for a 12-hour shift.”
In July 1995, Thompson pleaded guilty to 129 charges, including 61 sexual violations of women and young girls, and was sentenced to 30 years’ jail. It was the first time DNA had been used to catch a serial rapist.
You’d expect shows such as CSI that showcase forensic science would deter some offenders, but there’s no evidence of it, says Manning. “For some reason, crims keep leaving their DNA at crime scenes and we keep finding it – and finding them.”
“We had profiles from maybe half a dozen cases and knew we were looking for a serial offender.”
played a pivotal role in tracking the killer.
Twenty years on, he and Detective Sergeant Nick Salter, who spearheaded the Colin Mitchell investigation in the quarry case, say DNA was “a big nail in the lid” in the latest prosecution. It was supported by other important evidence – including CCTV footage of his silver Ford Mondeo arriving and leaving the scene, and tyre tracks in the quarry that matched those from his car – but none was as compelling as the profile on the gloves left at the scene. Scientists estimated it was 800 billion times more likely to have come from Mitchell than from anyone else.
INVISIBLE TO THE NAKED EYE
For the 1992 rape, however, there was nothing at the time apart from the victim’s testimony. “The DNA evidence solved that case,” says Salter. Although it is of little use in sex crimes where the issue is consent, Libby says it can be invaluable in “whodunits”. Mitchell’s explanation for his DNA being inside the gloves was that he’d tried them on at the Warehouse, but hadn’t bought them. The jury didn’t buy it, either.
From the start, the quarry attack was a high-priority investigation for the police and the ESR. The gloves were delivered to the institute’s Mt Albert headquarters a day after the attack, on Monday, February 27. Senior scientist Jason Barr, part of a team of a dozen scientists and technicians responsible for the forensic investigation of the most serious “person on person” crimes, including rapes and murders, managed the case.
The epithelial cells inside the gloves, invisible to the naked eye, were removed with double-sided sticky tape attached to a Perspex slide and dabbed over the fabric – much like we remove lint from clothes. The tape was then transferred to a small test tube, where it was suspended in a lysis buffer solution to break open the cells, releasing the DNA.
By Thursday, forensic biologists had not only developed a full profile from the gloves, but also had a match to the 1992 rape. For Barr, a 10-year-old primary school student in 1992, it was the first match to a cold case. Suddenly, an already high-priority file was code red.
“The balloon went up at that point,” says Salter. “Have we got a serial rapist?” A familial search of the databank – used in only the most serious cases – was launched, generating a list of names of people who could be related to the offender. None of them was, but the list nonetheless provided a flukish breakthrough.
One of the names on the list was for a “Mitchell”, and by that stage, police already knew that the owner of one of the silver Ford Mondeos registered in the Auckland region belonged to Colin Jack Mitchell. When his name was loaded into the police computer on March 7, details of his conviction and imprisonment for raping a sex worker in 1984 in startlingly similar circumstances popped up on the screen. The long-time truckie, president of the Onehunga RSA, was now at the top of the suspect list. Investigators had already whittled the list of thousands of Mondeos down to 77 still of interest – Mitchell’s name would at some point have been checked against the criminal database – but the lucky break gave them a few days’ head start. Mitchell had just five days of freedom left.
At 2pm on Friday, March 10, 11 police arrived at Mitchell’s flat in Onehunga with a search warrant, seizing his toothbrush, razor and the Mondeo. Mitchell, who lived alone and has no family barring a sister, had moved in about a year before. He was a hoarder and the place was a mess, says Salter. “He wasn’t expecting visitors.”
At the ESR, Barr stayed late waiting for the exhibits. A team was rostered on over the weekend to fast-track the analysis. Somewhat surprisingly, no trace of the victim was recovered from the Mondeo, although Mitchell was sufficiently forensically aware to have cleaned it the day after the quarry attack – a task caught on CCTV cameras at his Penrose workplace. Tests were conducted on eight samples from the car, but because the victim couldn’t remember where in the Mondeo she’d been – front, back, footwell or even the boot – scientists had nowhere to focus their attention. The time delay, and Mitchell’s cleaning efforts, had likely had an impact.
Ul t i mate l y, it didn’t matter, thanks to Mitchell’s toothbrush. By midday on Sunday, March 12, Barr emailed police: they had a match. He didn’t put it that way, of course, saying instead there was “extremely strong scientific support for the DNA from the glove and the toothbrush originating from the same person”.
UNDER ARREST
It’s satisfying for the scientists, says Barr, but their thoughts are always with the victims. “This isn’t a TV show; people have gone through harrowing things. We take our job incredibly seriously. Just remember that after you’ve finished watching the show or reading the story, the people involved are dealing with this for the rest of their lives.”
Within an hour of Barr’s email landing at Auckland Central police station, Mitchell was under arrest. At his trial in February, he continued to profess his innocence, but the jury didn’t believe him. For the prosecution, and the women he attacked who didn’t know his name, or couldn’t remember his face, DNA was perhaps the most powerful witness of all.
“I don’t think it’s necessarily wrong in principle to investigate volume crimes using DNA, but there needs to be a discussion about it.”