The Pennsylvania State Police arrested veteran paramedic Juan Torres on multiple counts of felony theft.
"It looks like he sold up to, possibly, 15 ultrasound machines and the one in our case was valued at about $35,000," State Trooper John Sunderlin said.
Police say Torres' asking price on eBay for the machine was under $7,000.
They traced one stolen from Riddle Memorial Hospital to a doctor in Argentina.
In June 2009, Torres worked as a paramedic at Riddle.
Riddle officials reported their Sonosite Titan missing during that same time frame.
Main Line Health owns Riddle and the Paoli Hospital, where two ultrasound machines were reported stolen in late October 2007.
According to eBay records, at least one of those Sonosites went up for sale on eBay a few days later.
Torres also worked at a private ambulance company located in Feasterville, Bucks County. The criminal complaint says that gave Torres access to Doylestown Hospital's emergency room where two Sonosite ultrasound machines were stolen last spring.
Police have traced both to sales on eBay from a seller called bioteched.
"Everything was related to his eBay account; investigation showed that through those eBay accounts, we were able to trace who he sold the ultrasound machines to," Sunderlin said.
As Torres headed to the Delaware County Prison Wednesday night, his bail was set at $50,000 with State Police still looking for up to 10 more ultrasound machines he allegedly advertised on eBay.