The defense for the Huntington Station man charged with stabbing a female neighbor to death attempted Thursday to undermine the strength of a key piece of evidence — a blood trail that led from the crime scene to the man’s house.

Adam Saalfield, 22, is charged with second-degree murder in the Oct. 12, 2014, slaying of Maggie Rosales, 18. In an attack captured on surveillance video, a man in a hooded sweatshirt followed her as she walked on Lynch Street, grabbed her from behind and stabbed her twice in the neck.

Although they lived on the same street, Saalfield and Rosales apparently didn’t know each other, lawyers on both sides agree.

Earlier this week, forensic scientist Thomas Zaveski of the Suffolk Crime Laboratory testified about marking 59 groups of blood stains that stretched a quarter mile from where Rosales was killed to in front of the house where Saalfield lived with his mother.

Zaveski testified that the blood likely dripped from a single source along a well-defined path.

But during cross-examination Thursday by defense attorney Craig McElwee of Hauppauge, Zaveski said two of the groups of stains were about four feet out of the path, in the center of Lynch Street rather than to the side.

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Later, during questioning by Assistant District Attorney Rafael Pearl, Zaveski said he believed those stains were not outside the path, but instead were a deviation of the same path.

Zaveski also said during cross-examination that not all of the stains were collected from the roadway and that sometimes stains close together in the same group were collected with the same swab.

Pearl said in his opening statement that although most of the blood came from Rosales, some had DNA from both her and Saalfield.

Also Thursday, retired Suffolk police Det. William Rathjen testified that he recovered Rosales’ cellphone, with earbuds plugged into it, from the edge of a massive pool of her blood. Pearl has said Rosales likely was vulnerable because she was listening to music when she was attacked.

Rathjen said her pocketbook was still there. Although she did not appear to have been robbed, the pocketbook contained just three pennies, some perfume, lip gloss and a receipt.

Another crime lab forensic scientist, Jeffrey Luber, testified about a search of Saalfield’s closet that discovered a pair of black boots. Stains on the top of the right boot appeared to be blood, he said.

Pearl has said the boot was stained with Rosales’ blood.

During questioning by McElwee, Luber said he checked all the doorknobs and doors at the Saalfield home for traces of blood and found none.