I.D. 1970s film, killer with heavy breathing or asthma

I’d love to find this movie, but I don’t remember what it was. Hopefully someone here will recognize it. Here’s what I remember:

A killer is stalking and killing victims. There were many moments in the film where we see the killer lurking somewhere, watching his victims from afar. There were pov shots from the killer’s perspective where you hear his breathing. The breathing was very heavy — I always thought he had a condition, maybe asthma, but it’s possible that it might have been just an effect for suspense.

I don’t think the killer spoke at all during the whole film.

I don’t exactly remember why he was killing people — I don’t think he was running around like a madman. He might have been a hitman. But he was relentless and didn’t stop pursuing his victims until they were dead.

I think we see the killer throughout the movie and there was no surprise the-killer-is-revealed moment. At the time, I thought the killer looked like Alan Arkin, but was not actually him. I might have thought this because he had a similar look to Arkin in “Wait Until Dark” (https://m.imdb.com/title/tt0062467/mediaviewer/rm2455547649/).

The other memorable scene is the final confrontation between him and this young woman. I don’t remember for sure if she was his only target or if there was a series of targets, but in the end, she was his main focus. They wind up at this industrial/scientific/lab/research/warehouse(?) place. She’s fighting him in I think a narrow area — a hallway or maybe a walkway or indoor bridge or catwalk. At one point, he appears to be dead. She turns away, possibly to talk to some people who have just entered, and we see behind her the killer is slowly getting to his feet. I know a lot of films have something similar, but in this movie, he gets up rather slowly, and as you’re watching her you slowly become aware of him (instead of him jumping up suddenly and grabbing her or whatever).

I don’t know if the whole movie was about trying to escape from this killer or what. I think there might have been a mystery/intrigue storyline, and this lead to the killer being there. In other words, the storyline might have about discovering why the killer was after people.

I saw this movie on broadcast tv in the mid/late 70s, but could possibly have been the early 80s. The movie would have been older by at least a few years, probably early 70s, possibly late 60s. I believe it was color and in English. I saw it on a non-mainstream channel (either channel 9 or 11 in the NY area). Every week for a period of time this channel showed a thriller/mystery film in the same time slot. They typically weren’t films I would have heard of but weren’t totally unknown — for example, another film they showed was “The Man Who Haunted Himself” with Roger Moore.

Thanks for reading all this! And thanks in advance for your help!!!