31-year-old Michael Henry pleaded guilty to 23 counts, among them purchasing the gun used by cop killer Andrew Thomas in the September, 2012 murder of Officer Fox.
Police say Thomas then killed himself with the same gun.
Henry's charges came down in October, shortly after Fox was killed. Pennsylvania Governor Tom Corbett made straw purchasing a crime around the same time.
Police say Thomas had a lengthy rap sheet that made it illegal for him to purchase a firearm. So, they say, he sought out Henry, who needed cash to fuel his drug addiction.
The two apparently met in rehab, and the charges show Henry purchased nine guns for Thomas. Police say only one gun was recovered.
Law enforcement officers showed their support in numbers Tuesday, along with Fox's widow. She is due to give birth to their second child in just a few weeks.
First Assistant District Attorney Kevin Steele said he wants the maximum sentence for Henry, who faces 42-84 years in jail.
"We're going to be asking for consecutive sentences on this," said Steele. "The impact that this individual has had on this family, on this community, on law enforcement in general, should equate to a very, very lengthy sentence to send a very strong message."
It could take up to three months to find out the judge's sentence.