Alan Zelencic

Deadly force

A mentally ill Queens man who had slashed his mother in their apartment was fatally shot by a cop after allegedly lunging at the officer with a 15-inch knife yesterday, police said. Alan Zelencic, 28, was hit twice in the torso but kept advancing on the cop and his partner as they retreated into the hallway of the Long Island City building, police said. Afterward, Zelencic slammed the door, locked it and remained holed up inside for about 50 minutes until cops determined it was safe to go inside. He was taken to Elmhurst Hospital Center, where he was pronounced dead. A police spokesman said the victim's sister, Lisa, called 911 at about 12:20 a.