Heuermann is charged with seven murders in one indictment.
Judge Timothy Mazzei is expected to rule soon on the defense's request to separate the case into separate trials, which is a move opposed by prosecutors.
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"This is an individual who has the specific intent to kill, to identify, locate, lure, obtain control over and murder multiple victims. That's the theory of our case, that's what our evidence shows," Tierney said.
He said that doing one trial instead of seven would save money.
"Obviously doing this case once instead of seven times it's going to be seven times more expensive."
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However, Heuermann's attorneys say that separating the charges is what's fair for their client.
"Each charge must fall or rise on its own. And you never want to use evidence that's unrelated, which would prejudice the jury's determinations. So that's in essence what the motion is predicated on. And hopefully the court agrees with our position," said Michael Brown, Heuermann's defense attorney.
No trial date has been set.
Heuermann's lawyers are also trying to get the judge to exclude DNA evidence in the case, which they argue has not been generally accepted as reliable in the scientific community.
A hearing on the DNA evidence, known as a Frye hearing, will start with one witness on March 28.
Other witnesses for that hearing will be scheduled in April. Suffolk County prosecutors say they expect to call at least four experts as witnesses.
"We have to establish that the science that we are seeking to use is generally accepted in the relevant scientific community, it was properly done and can be relied upon by the jury in making a determination in the case," Tierney said, explaining the hearing. "We know that DNA technology is used in a whole host of medical sciences. It is far from unproven. Quite the opposite, actually. This is an application of a very reliable and well-used science that we have to litigate. And that's what we will do. We feel confident in it."
Heuermann, who was arrested in July 2023, has pleaded not guilty to the murders of seven women whose remains were found discarded on Long Island between 1993 and 2011.
Tierney also said his office is now getting access to $13 million in federal asset forfeiture proceeds frozen by the Justice Department as part of an ongoing investigation into previous district attorneys.
"Unbelievably, seemingly out of nowhere, the investigation is over and we are going to be getting access to that money," Tierney deadpanned.
"It's amazing when the government is responsive, what can happen," he said.