At the end of a fast-moving day of developments, St. Louis, Missouri Police Chief Dan Isom announced the break on Thursday.
"We are confident based on the evidence we have that we have the killers of Megan Boken," Isom said.
Murder charges will be presented to the St. Louis Circuit Attorney's office on Friday, police said.
Isom credits what he calls "good detective work" for the arrests of the unnamed teenagers.
The first 18-year-old man was arrested Thursday morning in the St. Louis suburb of Bel-Nor. Police sources said that he was taken into custody in connection with some unsolved robberies. Among them: last Saturday's midday stick-up of Ms. Boken, who was in car parked on the side of street near St. Louis University where she had come to play in an alumni volleyball game.
The second 18-year-old man was arrested Thursday afternoon, along with a woman who is not thought to have been involved in the crime that stunned St. Louis residents for its cold-blooded execution.
Paul Boken, Megan's father, spoke out about the arrests late Thursday night.
"We're gratified with the progress they made in the case. It was a very difficult day today but with all of the people here for us, helped us get through it," he said.
As authorities in St. Louis worked the leads that would eventually break open the case, in the west Chicago suburb of Wheaton Thursday morning, Megan Boken's casket was carried into St. Michael's. The Roman Catholic church was filled with her family and friends who are overwhelmed by questions about what happened and why.
"I think this situation has highlighted what goes on daily in our country and it's just very, very sad to know that this can hit so close to home," said Mike Gresk, Wheaton mayor.
Outside the church in Wheaton -- where nothing can replace or return Megan Boken -- her friends left behind said justice matters.
"It's a relief I guess. I hope they catch the person who does it for her family and for her friends," said Maddie Defino, friend.
"We'll see how that pans out but that makes everyone feel better and, you know, just the family - they would appreciate knowing," said Bridget Fonke, friend.
St. Louis media are reporting that police traced a stolen cellphone from an armed robbery on August 10th in the same neighborhood where Boken was killed. Police and sources are saying that cellphone led them to the two people who are now in custody.