Even back in the early days of forensic DNA testing, the science was advanced enough to link the killings of two Long Island women who were strangled and bludgeoned to death months apart, a scientist testified Thursday.

Detectives already believed the killings of Rita Tangredi, 31, of East Patchogue, on Nov. 2, 1993, and Colleen McNamee, 20, of Holbrook on Jan. 30, 1994 were connected. Both had been killed and posed similarly — legs apart, and one or both arms above their severely beaten heads, prosecutors have said.

But Joanne Sgueglia, formerly of the Suffolk County Crime Laboratory, testified that in 1994 she established another link. The bodies of both victims, who worked as prostitutes, contained semen with matching DNA, she said during questioning by Assistant District Attorney Robert Biancavilla.

Sgueglia testified at the second-degree murder trial of Manorville carpenter John Bittrolff, 50. He was arrested in 2014 after more sensitive DNA testing suggested that the DNA in both bodies came from a relative of his. Detectives later got a DNA sample from Bittrolff’s garbage that matched the semen in the bodies.

The defense has argued that the DNA is not evidence of murder. Sgueglia said she also found DNA from at least three men in a semen stain on McNamee’s pants. During questioning by defense attorney Jonathan Manley of Hauppauge, she said it’s possible the stain could have contained DNA from as many as five men.

Sgueglia was the first of several DNA analysts who will testify at the Riverhead trial, now in its second month of testimony. As DNA technology improved and became more sensitive, evidence from the case was retested periodically.

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The DNA is the strongest evidence against Bittrolff, who was a well-liked neighbor in his community in the decades since the women were killed.

Biancavilla has argued that “wood chips” found on both bodies could be a link to Bittrolff because he’s a carpenter. But the witness who examined the material said it came from the victims’ clothes and were particles smaller than a millimeter — barely visible to the naked eye.

No tests confirmed they were wood, and some appeared to be plastic film or metal foil, according to testimony.