The apparently random, motiveless murder, on 9 May, shocked Italy to the core. Since then, key confessions have been withdrawn and watertight alibis have sprung leaks while staff at the law faculty have kept quiet, and ended up behind bars.
In a country with one of the lowest murder rates in the world - Mafia crimes excepted - indiscriminate assassinations by apparent loners are virtually unknown. That a law student of exceptional promise should crumple noiselessly to her knees on a crowded campus pavement and expire hours later in hospital was unthinkable.
But the initial shock has given way to disbelief as investigations uncover a network of omerta - the complicitous silence usually associated with the Mafia - in a university department where staff give every impression of having closed ranks. What remains to be seen is why.
Three low-ranking department employees are currently in prison, one charged with pulling the trigger and the other with complicity. One of the latter, Francesco Liparota, broke down under questioning and admitted to being with the alleged killer, Giovanni Scattone, and his friend Salvatore Ferraro when they shot, apparently at random, out of the window. Mr Liparota then retracted his testimony this week, after being released on house arrest and finding that his mother had received death threats.
But his original version has been confirmed by his mother, who said her son had confessed all to her. And it corresponds with the statement given to magistrates more than a month after Marta's death by assistant librarian Gabriella Alletto, who was on the other side of bookshelves when the shot was fired.
According to Ms Alletto, she reported the crime to department chiefs immediately. Her difficult decision to go to the investigators, she maintains, was made when it became clear that the department had no intention of coming clean. As a result, both the department head and the chief librarian have also been arrested.
"The university is corrupt through and through," commented one lecturer, who declined to be named. "And few departments have worse reputations than Philosophy of Law."
"Corruption" here refers to professors who attend the university only to pick up their pay cheques, delegating work and exams to low or unpaid minions such as Mr Scattone; to highly paid positions being given to under- qualified friends and relations; or to exam success depending on favours or payment.
But as they dig deeper, investigators are clearly having difficulty believing that members of a law department would protect the murderer to cover up administrative fiddles. And they are asking whether the silence surrounding Marta's death may prove to conceal something much more sinister.