Federal authorities on Thursday accused a Montgomery County karate instructor of sexually assaulting teenage students during sleepovers in the basement of his home and on trips to martial arts tournaments in Maryland and New York.

Prosecutors say three minors have alleged that Evan Burgess, 26, of Blue Bell, groomed them through interactions during lessons and pursued them on social media and during overnight hotel stays between 2014 and 2016.

All three reported waking up while sleeping in the same room with the instructor to find him performing sexual acts upon them.

Burgess was fired in May from DeStolfo's Premier Martial Arts Studio — the Plymouth Meeting karate training facility where he worked – after the boys' parents reported the alleged abuse to the business, according to court filings.

Yet, it was not until nearly four months later that Whitpain Township Police and Montgomery County Children and Youth Services began investigating the allegations after receiving an anonymous tip, the documents state. By that time he had moved from his parents' house in Blue Bell to Auburn, Mass. and found a karate teaching job there.

According to its website, the Plymouth Meeting studio offers instruction for students as young as 3 years old up to adulthood. Burgess, authorities said, had been involved there for nearly two decades, first as a student who enrolled in karate lessons at the age of eight and later as a paid instructor.

Andrew Kasmen, a lawyer representing business, said Thursday that owners, Fred and Dena DeStolfo, first learned of the accusations against Burgess in May and immediately met with parents for the three students.

Each made only vague claims that Burgess had had inappropriate contact with their sons, Kasmen said. Still, the lawyer said, the DeStolfos immediately reported it to Children and Youth investigators and Plymouth Township Police. Kasmen did not know whether either office pursued the investigation from there.

"It's not their fault," Kasmen said of the DeStolfos. "Nothing occurred at their studio at all. It was all out-of-state things." He added: "God forbid, if these [allegations] are proven to be true, the DeStolfos are as shocked about this as anyone."

Burgess' lawyer, Ron Greenblatt, described the allegations as unsubstantiated and his client as wrongly accused.

"This young man maintains a sterling reputation by all those who know him best," he said. "He adamantly denies any inappropriate contact with anyone and looks forward to addressing  this matter in court. … We are confident that once all the facts are revealed he will be fully exonerated."

Court records indicate that when approached by Whitpain investigators earlier this month, Burgess admitted to sharing beds with minors from the karate studio on several occasions but denied abusing anyone.

His accusers, however, say otherwise.

The complaint filed in federal court in Philadelphia sketched out a classic scenario of predatory grooming.

His accusers described Burgess – whose Facebook page is plastered with photo galleries of his students, some posing shirtless — as an unusually attentive teacher. He often asked his underage students for their cell phone numbers and social media accounts so he could text or contact them through platforms such as Snapchat, they said.

"Burgess was closer to the younger students than any other karate instructor at the studio had ever been," the complaint says one accuser told investigators. "He would hang out with the students, go to the movies with them and have them sleep over at his parents' house," where he was living at the time.

And during frequent out-of-town trips to karate tournaments, it was common for Burgess to ask to share hotel rooms with his students and their parents, claiming he could not afford a room of his own.

It was on one of those trips to a 2016 tournament in National Harbor, Md., that one accuser says he woke up to find Burgess grinding against him in bed, grabbing at his penis and attempting to initiate sex.

The boy, who was 16 at the time, told investigators he immediately jumped out of bed, left the hotel and spent the rest of the night wandering  the streets of the unfamiliar city.

Another student said that when he was 15, he woke up while staying in a hotel with Burgess during a 2014 tournament in Long Island, N.Y., to find his teacher groping his genitals through his clothing, according to the complaint.

Burgess' third accuser, the affidavit states, said his abuse occurred during a sleepover at the karate teacher's parents' house. He woke up in the middle of the night to find Burgess performing oral sex on him, he said.

Whitpain investigators  arrested Burgess Friday as he returned home to Montgomery County to visit his parents over Thanksgiving weekend.

He posted a $75,000 bail the same day and had returned to Auburn to resume teaching by the time federal prosecutors adopted the case and re-arrested him in Massachusetts on Tuesday.

As of Thursday, he remained in federal custody in route to Philadelphia, where he is expected to stand trial on charges of transporting minors across state lines for the purposes of illicit sexual activity.