Matt had no ID, so she would describe him the best she could: his age, his height, his blue rubber wristband emblazoned with "Puerto Rico."
Finally, a call to Boston Medical Center yielded a match. The mention of the wristband confirmed it was him.
It was 3 a.m. by the time Cruz made it to the hospital and saw Matt.
"I was devastated. I was shocked," she said on Thursday. "It just didn't look like my child."
Matt Cruz, a Neshaminy High School sophomore, was one of 42 passengers on the bus when it struck an overpass on Soldiers Field Road in Boston. The road is a major crosstown connector to the Massachusetts Turnpike, and has several low overhangs and signs warning drivers.
The bus struck a overpass and its roof caved in, injuring more than 30 people aboard.
Matt Cruz, who ran track at Neshaminy, was among the most seriously injured. Another passenger, 43-year-old Iris Sykes, a chaperone, suffered severe head and spinal-cord injuries, according to her attorney, Thomas Kline. She was transferred from Boston to a Philadelphia-area hospital last week and discharged Thursday, Kline said.
Except for a short trip home, Megan Cruz has been with Matt in Boston since the accident. Matt remains in critical condition, with several fractured vertebrae. He had fluid in his lungs, a severe laceration to his scalp, and pneumonia. At this point, his injuries have left him incapable of moving.
On Thursday, Matt underwent surgery to insert a tracheostomy tube. His mother spoke by phone during the procedure.
When not sedated, she said, Matt is alert and aware, watching SportsCenter on television and able to alert doctors if he is in pain.
"He's still Matt," she said.
Still, his recovery is expected to be arduous, she said. Her son still needs a ventilator to breathe, and is unable to speak, communicating by mouthing words or moving his eyes.
He has become a popular patient among staff members, Cruz said, and uncles, aunts, grandparents, and cousins have visited. Her 10-year-old son is staying at a friend's house in Bucks County so he can keep going to school.
No date has been set for Matt's release from Boston Medical Center, even to a hospital closer to home.
"The hardest part is just watching him suffer, day in and day out, and he did nothing to deserve it," Cruz said. "He did nothing wrong."
The Cruz family has sued the bus company, Calvary Coach of West Philadelphia, and driver Samuel J. Jackson, 66, alleging that Jackson should have seen height-restriction signs.
Attempts to reach Jackson on Thursday were unsuccessful, as were efforts to reach Erica Waller-Hill, director of the nonprofit group that organized the trip, Destined for a Dream. Waller-Hill is not named in the lawsuit.
After the crash, Raymond Talmadge, owner of Calvary, told NBC10 that Jackson was looking down at his GPS and missed the signs. Reached by phone on Thursday, Talmadge declined to comment.
Megan Cruz said on Thursday that she knew the complaint had been filed and that she hoped her son could come home soon.
"It's just an awful situation all the way around," she said.
Contact Chris Palmer, 609-217-8305, firstname.lastname@example.org, or follow on Twitter, @cs_palmer