Subways on alert

A mentally disturbed German man yelled “Infidel, you must die!” as he fatally stabbed one man and wounded three others at a Bavarian train station Tuesday — prompting the NYPD to beef up security in the Big Apple subways.

The 27-year-old unemployed carpenter, who received psychiatric care Sunday, also shouted “Allahu Akbar” — Arabic for “God is Great” — as he assaulted his first victim, Reuters reported.

“He’s a crazed psychopath,” a police investigator told AFP.

The suspect had a 4-inch survival knife tucked into his belt when he was nabbed early Tuesday outside the Grafing Bahnhof station near Munich, authorities said.

One victim, a 56-year-old man, died at a hospital. A 58-year-old man was badly injured, while two other men, ages 43 and 55, suffered non-life-threatening injuries.

The suspect — named only as Paul H. — admitted to the crime, according to the Munich prosecutor’s office.

During an appearance on CNBC’s “Squawk Box,” Police Commissioner Bill Bratton said the NYPD responded to the attack by increasing its presence in the subway system.