So a police officer sat down at the woman's computer to see the next threat himself.
By July, the FBI was knocking at the door of Hart, a former SEPTA employee now being held in jail. On Monday, he will be sentenced in U.S. District Court for a string of electronic attacks on the woman, her friends, and her family. He pleaded guilty in November.
"For about a month, when all the harassment was going on, I would sit in my room and pray to God that it would stop," the 24-year-old woman, who lives in California, wrote in a victim's statement. Her name is redacted from sentencing documents.
In the course of a few hours one evening last year, prosecutors believe, Hart dispatched a sewer repairman, a pizza deliverer, and an electrician to her father's house.
After a short relationship - initiated on an online dating site - Hart reacted with fury when the woman announced she was moving from Philadelphia to take an internship at Lawrence Livermore National Laboratories in California.
First, he threatened suicide. Then came the stalking.
The self-deleting e-mails were an unusual touch: Even the experienced federal prosecutor in Philadelphia had not encountered it before.
Hart also used a second tactic, called "spoofing," to make harassing calls that recipients could not trace to his telephone number.
Using "SpoofCard.com," one of many Internet services that permit callers to hide their phone number and even change the sound of their voice, Hart made calls warning the woman that she had 10 days to leave California "or else." In another call, he said, "You're going to [obscenity] die."
Thanks to modern electronics, that wasn't all.
Using passwords obtained while they lived together, Hart canceled a doctor's appointment, changed the passwords on the woman's e-mail and Facebook accounts, took control of her bank accounts, and deleted her application to take the Medical College Admission Test.
Assistant U.S. Attorney Michael Levy is asking for a sentence of at least 57 months, a year above the federal guidelines. "To say that this defendant has serious emotional problems when it comes to dealing with women is an understatement," he has told the judge.
He also offers some advice: Completely revise a password whenever you believe it is compromised. And be careful with whom you share a password.
Hart's attorney, federal public defender Mark T. Wilson, did not return messages seeking comment.
Hart pleaded guilty to stalking and unauthorized use of a computer. Such crimes are usually prosecuted in state court, but he is facing a federal judge because the victim worked at a federal institution, Livermore, whose internal police force the woman had initially contacted.
Among other scientific work, Lawrence Livermore is the nation's top nuclear-weapons research lab, though the woman, a biology and premed major, was not employed in that research.
Hart has previous convictions for forgery, and in 2003 he was convicted in Burlington County "for almost identical" stalking charges, Levy said. In 2005, he was convicted for sneaking into a women's bathroom at Immaculata College and videotaping students as they used the toilet. He initially received probation, but within 18 months he was in violation and served time in jail, according to court documents. He is in Chester County Jail for again violating his probation.
When FBI agents searched his Philadelphia apartment, they discovered a telescopelike object called a "peephole reverser."
"The agents tested it and determined that it enabled a viewer to look into an apartment through the peephole," according to court documents.
"The Federal Bureau of Prisons does have counseling programs," Levy said in an interview, "and he clearly needs counseling. I don't know if he would be cured."
Levy, who has wide experience handling computer crime, said it was the first case he had handled involving self-deleting e-mails.
No one from the mail service Hart used, BigString in Red Bank, N.J., returned calls or messages seeking comment.
The company is in financial trouble, according to corporate records, but at least a half-dozen other firms offer such services, according to their websites. Various technology is used. BigString promises that once the recipient clicks on the message sent through its servers, the mail will "self-destruct" within a specified time period.
On its website, the firm adds, "The mail, while looking like every other mail, will print nothing when the receiver clicks print on the computer and show nothing if the receiver tries to save the text or image."
The second technique Hart used is more common. Spoofing has been controversial enough that Congress last year made it illegal to hide the origin of a telephone call "unless a legitimate business reason exists," according to pending Federal Communications Commission regulations.
Meir Cohen, president of SpoofCard.com, said that despite the firm's name, its intent is to provide legitimate services. As an example, he cited an on-call physician who may use a personal cell phone to contact a patient but wants return calls to go to his office or answering service first. The doctor can have one of those numbers appear on the patient's telephone instead.
"The vast majority of our customers use it as a tool to protect their privacy," Cohen said. "A large portion of customers are really women who want to protect their privacy and don't want [stalkers] to have their numbers."
Cohen, who was familiar with the Hart case, said, "My heart goes out to the victim."
SpoofCard.com cooperates with law enforcement, he said, and "we will hand over records if we are subpoenaed."
Contact staff writer Nathan Gorenstein at 215-854-2797 or email@example.com.