The more they dig, the more the dirt piles up.

The massive NYPD ticket-fixing investigation has uncovered evidence of far more serious crimes, with cops allegedly making potential felonies go away for fellow officers, it was revealed yesterday.

Shameless cops tried to squash domestic-violence complaints against off-duty colleagues before department brass got wind of the incidents, according to DNAinfo.com.

Some officers also tried to erase other cops’ drunken-driving arrests.

And horndog cops were even overheard ordering and paying for prostitutes over the phone, the report said.

Probers listening to secret wiretaps of at least 30 cops have also learned that the scandal extends to all five boroughs and to the highest levels of the NYPD.

The Web site said there 502 cases under scrutiny: 380 in The Bronx, 55 in Manhattan; 30 in Queens; 30 in Brooklyn and seven on Staten Island.

Targets being investigated include a chief, an inspector, four deputy inspectors, four captains, 10 lieutenants, 25 detectives and 30 sergeants, the site said.

The rest are police officers, and many are union delegates, DNAinfo reported.

Investigators found 240 tickets from last year in the locker of one union rep in lower Manhattan, the report said.

Sources said the dirty cops were rewarded with cash, booze, pricey restaurant meals and tickets to ballgames.

“There is a clear distinction between discretionary [fixing of tickets] and taking gratuities,” a union official told DNAinfo.