Magisterial District Judge David Murphy didn't know when to quit, Delaware County authorities say.

Even though detectives were investigating dozens of shady signatures on Murphy's nominating petitions, the Aston Township judge still ran for re-election in November - and won in a landslide.

And even though Murphy has been on paid leave from his $80,927-a-year job since August because of the investigation, he deposited the first paycheck of his new term last month.

Bad move.

That deposit was exactly what prosecutors were waiting for, so they could allege that Murphy forged the signatures at least partially for financial gain, District Attorney G. Michael Green said.

Yesterday, Murphy, 57, a Democrat-turned-Republican who was elected in 1991, and his ex-girlfriend, Deborah West, 53, were arrested on hundreds of felony charges, including forgery, identity theft and criminal conspiracy.

Green said the charges stem from an "extensive investigation" that began with a "reliable" tip last summer.

Detectives interviewed more than 225 people and hired a handwriting expert who concluded that dozens of names on Murphy's petitions were signed by Murphy and West.

"Here, it's the candidate participating in this, which makes a difference, a significant one," Green said.

Green said Murphy and West have a "personal relationship."

A source told the Daily News that they had been romantically involved, but that the relationship ended last year.

Murphy's attorney, Art Donato, declined to comment yesterday after his client was arraigned in Media by Bucks County Judge John J. Rufe. West's lawyer, Vicki Herr, said she is hoping West could enroll in a program for first-time offenders.

In January, an unnamed witness told investigators that West was blackmailing Murphy by "holding something over his head," according to court documents. That claim has not resulted in criminal charges, but Green said it's still under investigation.

"There was no blackmail," Herr said.

"That's from an unnamed source and there's no validity to it," she added.