A loud boom thundered about 8,000 feet above Boulder Saturday as two small planes collided, killing three people: pilot Bob Matthews, 58, a longtime Boulder lawyer, his brother, Mark A. Matthews, 56, and Evergreen pilot Alexander Howard Gilmer, 25. Bob Matthews’ Cirrus SR20 plane crashed with the Piper Pawnee that Gilmer used to tow a Schweizer 2-32 glider. Rueben Bakker, the pilot of the glider, and his two passengers, a woman and her 11-year-old son, survived.

Bakker saw the Matthews’ plane “out of the corner of his eye,” says Jennifer Rodi, the National Transportation Safety Board’s lead investigator, and cut the tow line just in time, navigating through a ball of flame and landing safely at Boulder Municipal Airport about three miles southeast of the crash site, reports the Daily Camera.

Meanwhile, families and friends are mourning the three who lost their lives.

“He was your classic great guy,” Neal Cohen, a law partner of Bob Matthews, says of his friend. “He was the center of gravity for his friends. He was devoted to his family. We’re all just incredibly stunned.”

With no black box data, investigators are left to rely on video, photos, and witnesses’ testimony to determine what led to the crash (via The Associated Press). They also have some radar information from the Cirrus plane for their probe, which could last six to nine months, notes 9News, although a preliminary report could be issued much sooner.