Police waited almost 3 ½ hours to even request an off-duty cop submit to a breath test after he fatally mowed down a Bronx grandmother while allegedly driving drunk, prosecutors said today

“It was almost 10:00 A.M. before the defendant was even asked to submit to a Breathalyzer test, which was refused,” said Steven Reed, a spokesman for Bronx District Attorney Robert Johnson.

That delay meant Detective Kevin Spellman was not compelled to give a blood sample to investigators until around noon Friday – a full 5 ½ hours after striking Drana Nikac at around 6:30 a.m.

Prosecutors were forced to obtain a search warrant from a judge, but could not even begin the legal process until Spellman refused the test.

The results of the blood test had still not come back late yesterday, officials said.

NYPD officials did not immediately respond to questions about the delay.

Spellman, 42, a 23-year veteran assigned to an elite fugitive task force, was charged with vehicular manslaughter, criminally negligent homicide and DWI following the wreck on Kingsbridge Avenue in the Bronx.

The episode was alarmingly similar to another fatal DWI crash involving a cop who left a pastor’s daughter dead in Brooklyn. In that case, it took seven hours before Officer Andrew Kelly was made to give a blood sample. It later came back negative for alcohol, but he was charged anyway and other officers suspended for an alleged cover-up.