An open plea means that there is no prearrangement between defense and prosecution on the terms of the sentence.
Becker could face up to 10 years in prison on each of the 10 gun-related thefts, which are second-degree felonies. He also could spend many more years behind bars in connection with the other charges.
Vincent P. DiFabio, Becker's attorney, did not respond to a phone call.
Before he resigned in June 2011, Becker served as custodian of the evidence room. He stole items and then resold them to support a drug habit, police said.
From 2003 to 2011, police alleged, he stole 10 firearms, including a German Luger pistol and a 12-gauge shotgun. Frederiksen said all 10 guns had been recovered, from as far away as Texas.
Becker also took $18,000 in cash, an Omega watch valued at $2,700, and narcotics worth more than $2,000 from the locker, police said.
He was charged with one count of drug possession.
Between December 2009 and January 2011, Becker coerced four civilians into purchasing drugs as part of what he said was an undercover operation, said Frederiksen said.
"He would approach individuals and convince them to become confidential informants for him in a supposed drug investigation, but in reality, he was simply keeping what they were obtaining," Frederiksen said.
Becker is free on $10,000 bail. As part of the bail agreement, he can have no contact with the four civilians. No date has been set for sentencing.
Contact Bonnie L. Cook at 610-313-8232 or bcook@phillynews.com. Read her "MontCo Memo" blog at philly.com.