They pointed guns and were wearing dark clothes, gloves and black ski masks.
"Where's the safe?" they shouted.
The four-day trial included detailed testimony from the 14-year-old daughter of the man who had been followed. She was at the house with only her 21-year-old brother when the home invasion occurred.
"They had him on a tracker," Assistant State's Attorney Donna Fenton told jurors. "They found out where he lived, and they knew when he would be away from the home."
The gunmen sneaked up on the siblings by slipping into the garage as the door closed after the brother and sister returned from a trip to get dinner.
The intruders used thick, plastic zip ties to bind both victims' hands behind their backs. One robber pressed his gun against the brother's head, marching him through the home looking for cash.
The 14-year-old was held facedown on the garage floor at gunpoint, her mouth covered by duct tape.
"I was positioned to lie completely flat," she testified. "I was really nervous about what might happen. So I tried to get on my knees, or tried to reposition myself. But he told me to lay completely flat."
Several times, she was lifted by her collar, moved around the garage and ordered back on her stomach — although at one point one of the armed men said: "We won't hurt you, baby girl."
The robbers took her iPhone and $6,000 cash from the house and fled the home, in the western part of the county in the Darnestown area. The victims called 911.
Among the evidence collected: duct tape found to have Carroll's DNA.
Prosecutors also told jurors the tracker had been stealthily attached to the gambler's car, likely while he was at the Horseshoe casino in Baltimore. The suspects not only used it to follow him, Fenton said in closing arguments, they also used it to learn his later movements.
Jurors started deliberations just before 10 a.m. Friday and ended about three hours later with guilty verdicts on all counts against Carroll: home invasion, two charges of armed robbery, two charges of first-degree assault and one charge of using a handgun in the commission of a felony.
He stood, without noticeable emotion, as the verdict was announced and turned his head to his family members in court. Carroll will be sentenced at a later date.
Authorities have yet to learn who the second robber was. The Washington Post is not identifying the juvenile witness because of concerns over her safety. Neither of the victims' parents testified.
"I was pretty distressed about this for a while," the daughter, now 16, said on the stand.
Carroll did not testify. "He maintains his innocence and looks forward to a vigorous appeal," one of his attorneys, Andrew Jezic, said.
Jurors also heard key, and colorful, testimony from another casino patron, Gary Weaver. He told of being followed to Montgomery County after a big win — by a dark Acura that prosecutors said was linked to Carroll — and offered details of his regular spot at the craps table.
He testified he knew Carroll because he'd sat beside him at least two dozen times at craps tables.
"He was nice guy. I liked him," Weaver said, answering questions from Carroll's attorney.
"And he appeared to be successful at what he was doing?" Jezic asked.
"No, he was losing his ass. Excuse me," Weaver said.
"Say it again?" Jezic asked.
"He was losing a lot of money," Weaver answered. "Sorry, judge."
"No problem," responded Montgomery Circuit Judge Michael Mason.
Weaver told jurors of a lucky night he'd had at the casino in 2015 and what happened after he cashed out. "I had about 20 grand on me," he said.
Weaver said that as he drove home to Montgomery County, he felt he was being followed. He said he maneuvered to try to lose anyone trailing him and eventually was able to separate himself from the car at the entrance to his gated community.
Detectives at the Montgomery County Police Department investigated Weaver's account and collected records of his E-ZPass electronic toll card that he used on the Intercounty Connector that night. The detectives learned of another E-ZPass that had been used just behind him, which they linked to a car Carroll often drove, prosecutors told the jury.
Carroll was not charged in that separate alleged incident, but the judge permitted prosecutors to present the account to jurors to show a possible pattern of behavior by Carroll.