The way she saw it, her life had two roads: Be a tenured professor or drive a bus.

Amy Bishop, the troubled neurobiology professor at University of Alabama, Huntsville, accused of shooting three colleagues dead, saw firsthand what happens to academics tossed out of the ivory tower — a job befitting a high-school dropout.

“That’s what happened to one guy that didn’t get tenure, and he is driving a courtesy shuttle,” James Anderson, Bishop’s husband, told The Post yesterday in explaining what may have prompted his wife to murder her colleagues.

“His work later went on to help two guys win the Nobel Prize in chemistry,” he added.

Bishop — who shot her brother dead in 1986 under murky circumstances and was questioned in 1993 over a mail bomb sent to her Harvard doctoral adviser — was being tossed from the prestigious science school at semester’s end.

She feared she’d end up like Douglas Prasher, a brilliant molecular chemist who had to abandon his research in 1994 when his funding dried up.

His colleagues went on to the win the Nobel Prize in chemistry in 2008 based on his research. Prasher currently drives the courtesy van for a Huntsville Toyota dealership.

“There is always life after tenure,” a shocked Prasher told The Post after learning that his misfortune had become a cautionary tale, even though his problem was with funding, not tenure.

Prasher said he never crossed paths with Bishop — whose tenure application was just rejected after she spent six years at the school.

Bishop had an attorney fighting her case and had other job prospects, her husband protested.

Anderson said it is still a mystery what actual “trigger” set off his wife, who neighbors told reporters was intolerant of noisy kids and even the ice-cream truck.

Anderson told the AP he had recently gone to a shooting range with Bishop but said he didn’t know where she got the gun used in her attack.

Anderson told the Chronicle of Higher Education that she may have received an e-mail, which he called a “nastygram,” last Friday confirming her tenure was rejected.

That same day she allegedly stormed into a faculty meeting firing a 9mm handgun at six colleagues, including Biology Department Chairman Gopi Podila.

While Bishop, 44, remains in police custody, her husband vehemently denied reports that his wife was behind the attempted bombing of her Harvard adviser, Dr. Paul Rosenberg, 17 years ago.

“There were dozens of subjects of the investigation. We were never suspects. There were never any indictment and never any arrests,” Anderson told The Post. “They were chasing every lead at the time, trying to find out what was going on and came up with nobody.”

Somebody mailed Rosenberg, who reportedly was going to give her a poor evaluation, a package containing a pipe bomb, but he called cops before the device detonated.

“We knew she had a beef with Paul Rosenberg. And we really thought it was a really unbelievable coincidence that he would get those bombs,” Sylvia Fluckiger, a lab tech who worked with Bishop told the Boston Globe.

Years earlier, a 20-year-old Bishop shot dead her 18-year-old brother with a shotgun in their Braintree, Mass., home.

Although she fired three times, the local police — who employed Bishop’s mother in the personnel department — believed her story that the shooting was an accident.

Much of the paperwork from the investigation has disappeared.

Families of the victims were outraged that Bishop was even hired by the University of Alabama in 2003.

“I think they need to do a little more investigation when coming down to hiring teachers and things like that. Maybe looking a little deeper into their past about certain things,” said Melissa Davis, whose stepmother, Maria Ragland, an associate professor, was killed.

In Huntsville, Anderson said their four children are “barely hanging in there” as they try to make sense of violence.

After the shooting, Bishop calmly called her husband asking to be picked up. They had a date night scheduled. They were going to get coffee.

Later, from the police station, she reportedly asked her husband if the kids had finished their homework.

“We will comment in the near future,” Anderson said. “Now I’m asking everyone to back off and let us sort everything out.”

chuck.bennett@nypost.com

