Washington (CNN) -- The District of Columbia principal who was found shot to death in his home last month met his alleged killers on a phone chat line, authorities said at a news conference Monday where they announced arrests in connection with the slaying.

Two men have been charged in the killing of Brian Betts, 42. They have been identified as Alonte Saunders, of an unknown address, and Sharif Tau Lancaster, who resides in the District of Columbia, police said.

The suspects, both 18, have been charged with first degree murder, armed robbery and the use of a handgun in a felony crime of violence, according to Officer Melanie Brenner of the Montgomery County, Maryland, Police Department.

Brenner said charges against a third unidentified suspect, also 18, are pending. Earlier, police said a fourth person was arrested in connection with the slaying of Betts. Artura Otey Williams, 46, was charged with two counts of knowingly receiving a stolen credit card with the intent to use it.

Betts' body was discovered in his Silver Spring, Maryland, home, on April 16 after he didn't show up for work at Shaw Middle School. At Monday's news conference, Police Chief J. Thomas Manger said "one or more of the suspects was connected with Betts after he (the victim) used a phone chat line." Manger said it was a "sex line" and that the call was made on the night of Betts' death.

"We did not believe that this was just a random case and as far as we could tell there was some connection made via this chat line," Manger said, "but whether or not the victim had previous contact with the suspects before, we don't know that."

Lancaster's fingerprints were found in the victim's home near the scene of Betts' death, Manger said. He said fingerprints belonging to Saunders were recovered on the exterior and interior of Betts' vehicle, which was found abandoned on a Washington street two days after the killing.

Manger said the investigation remained very active and asked people to come forward with more information.

He also had a warning to anyone who interacts with strangers on the internet or phone chat lines. "You just never know who you may meet up with," he said.

The death of Betts, who was a popular educator among faculty and students, has shaken the community.

"He was an inspirational leader for the teachers and the students, and that leadership was bringing results," Chancellor Michelle Rhee of the District of Columbia Public Schools said in a statement.

"He knew what the children under his care were capable of, and he was determined to show them how to get there. Brian Betts' death is an incredible loss of a young and dedicated school leader."

AC360° blog: Online tributes for slain principal

Past and current students, as well as employees, have posted online their thoughts and memories of the slain principal.

"Mr. Betts was one of those teachers you could never forget," wrote one former student. "Yes, he was a teacher, a figure of authority, but he felt more like an older brother, and made us feel comfortable about coming to him about almost anything ... Our area has lost an amazing person."

CNN's Gabriel Falcon and Rick Martin contributed to this report.