Even at 19, Matthew Lowry was clean-cut and cautious, unwilling to do anything that might sabotage what he always wanted: a law enforcement career like his father’s.

That’s how Joann Green remembers Lowry, the FBI agent who was found in late September slumped over the wheel of an unmarked FBI vehicle with heroin and guns inside.

Green, whose daughter dated Lowry for a year when he was in college, considered him an ideal boyfriend — handsome, polite and ambitious. “I thought he was dropped from the heavens,” she said.

She and her daughter, who declined to be interviewed, were stunned when they learned that Lowry was under investigation for possibly stealing and using heroin seized as evidence — a scandal that has prompted two federal judges to toss out charges against nearly two dozen members of what prosecutors allege were two dangerous and sophisticated drug rings.

“He was strait-laced, a proper child,” Green said. “How in the world did it get to this?”

The answer to that question is anything but clear. Lowry, 33, has been suspended from his job, said his attorney, Robert C. Bonsib, but not charged. He is cooperating with investigators, who have said little about what they think led to the agent’s alleged actions.

Bonsib decried some of the aspects of the Lowry investigation as “grossly overblown” and said that Lowry is “devastated by what has occurred here.”

While prosecutors and investigators sort out whether his actions have affected additional cases, those who knew him growing up in Upper Marlboro, Md., are having a hard time reconciling the allegations with the young man they knew.

“He was a typical student with decent grades. There were no major issues,” said George Hornickel, director of Grace Brethren Christian School, a small, private school in Clinton, where Lowry attended high school and graduated in 1999.

“We are a Christian school. We teach morals, honesty and all good things,” Hornickel said. “We understand that not all graduates who leave here embrace all the values. We try to get kids to follow Christ.”

From a young age, Lowry wanted to go into law enforcement like his father. William Lowry was a Prince George’s County police officer for 27 years before heading security details for two NFL teams, including the Washington Redskins. He is an assistant police chief in Anne Arundel County. His wife, Sylvia, is listed as a Sunday school teacher at the First Baptist Church of Upper Marlboro.

Of William Lowry’s three sons, Matthew was the only one who wanted his own police badge, friends recalled. Some said he was his father’s favorite. (One son also ended up following in William Lowry’s footsteps, working in stadium operations for an NFL franchise.)

Through an Anne Arundel County spokesman, William Lowry declined to comment for this article. Sylvia Lowry and her two other sons did not respond to e-mails and voice-mail messages seeking comment.

In his high school yearbook photo, Lowry is wearing a dark suit jacket. Next to the picture is a citation from Matthew 5:9: “Blessed are the peacemakers, for they shall be called the sons of God.”

At Grace Brethren, Matthew was a varsity soccer player and wrestler and a member of the National Honor Society. Yet he did not make a lasting impression on many of his classmates, based on conversations and e-mail exchanges with at least a dozen former students. The school has slightly more than 600 students in pre-kindergarten through 12th grade.

“He always seemed to follow the rules and not cause any trouble,” said one fellow graduate, who described Lowry as an acquaintance. “He had a pleasant demeanor and was a quiet type. He didn’t seem to be one [who] had trouble with school or grades.”

Lowry stayed close to home for college. He earned a bachelor’s degree in criminology from the University of Maryland in 2002, school officials said.

Later, when others in their 20s were busy wallpapering Facebook with party photos or sending the occasional off-color tweet, Lowry did not leave much of a virtual trail. He does not have a Facebook, Twitter or LinkedIn profile.

Joann Green said that was probably by design, given his law enforcement aspirations.

His focus and drive at 19 impressed Green, then a single mother, who was overjoyed when her daughter brought Lowry home to meet her.

But Green said she failed to convince her daughter of that, and about a year later the couple broke up. Lowry went on to marry Shana Khachab, a senior territory manager for a global pharmaceutical company whose family has operated several restaurants in the Washington area. Khachab also coached a competitive cheerleading squad at South River High School in Edgewater, Md.

The couple bought a townhouse in Odenton, Md., and later purchased a three-bedroom townhouse off Florida Avenue in Northwest Washington.

His attorney said Lowry graduated with honors from the FBI Academy, where students receive at least 18 hours of ethics training.

For several years, he worked for the FBI in Washington in a support-personnel position, law enforcement officials said, before becoming an agent about five years ago. He was part of a task force that focuses on crime along the borders between the District, Maryland and Virginia.

Before and after he became an agent, he would have been polygraphed and tested for drugs, a circumstance that has raised questions about how any illicit drug use could have slipped by his superiors.

Current and former agents said that cases of misconduct on the scale of which Lowry is accused are extremely rare. If the allegations prove to be true, he could face years behind bars. In 1995, Kenneth R. Withers, an FBI agent in Philadelphia who confessed to taking drug evidence to sell, was sentenced to 25 years.

Prosecutors have not revealed how Lowry’s actions unraveled cases for some defendants and not others. Attorneys for several co-defendants who are still in prison have pressed for a more detailed accounting, to no avail.

Prosecutors might not receive answers until the FBI’s Office of Inspector General completes its investigation.

Green has questions, too. She wondered how such a careful young man reached the stage at which he was willing to risk “his lifelong dream.” Were there warning signs that were missed?

“Obviously,” she said, “something went terribly wrong.”

Adam Goldman, Jennifer Jenkins, Peter Hermann and DeNeen L. Brown contributed to this report.