"No Threat Of Pain Or Death Could Stop These Strange Creatures From Outer Space" Here is a Monarch Books paperback original from 1963. Ivar Jorgensen is a pseudonym used by several writers, in this case it is classic science fiction author Paul W. Fairman.
A pedestrian is hit by a cab in downtown Manhattan and taken to Park Hospital. "And far out in space, among the yellow pinpoints we call stars, a signal was registered - Something has gone wrong."
Dr. Frank Corson treated the man for a broken leg, but, was he mistaken the man had two heartbeats? The blood was also strangely inhuman, a synthetic plasma. No identification.
Brent Taber heads a secret government force briefing the Navy, Air Force, Treasury, FBI, and State Departments on what has been discovered. Eight other clones have been found in cities across the United States, exact replicas of each other from identical fingerprints to overdeveloped brains for telepathic communication, yet outwardly appearing as pleasant men in blue suits.
Frank confides his concerns to his self sufficient girlfriend Rhoda, but is shocked to see the same man walking around New York the next day! Yes, the tenth android has the cold judgement to make the broken ninth nonfunctional - and still complete the task, for he admits they know what they were created for. The other androids met with strange accidents or malfunctions, as if they were trying to discover how to live in our world. In a quest to extract information from Frank about the clone autopsies, the android casts a hypnotic spell over Rhoda. He has never seen a woman before. Quickly he is discovering there is a difference, and Rhoda is powerless in his arms - but seems to be having a pretty good time.
The story flashes back and forth between Frank and Rhoda, Brent and the government agencies, and the quest of the tenth android, detached from the killing needed to complete his task. Being 1963, there is a Russian invasion theory, but this stays in the medical and scientific realm, including some interesting theories of synthetic emotion and transference. The men are not men; machines but not machines. If they walk and breathe but hold no emotion, are they alive?
But you aren't reading this for edification.
If you like speculative science fiction of alien invasion, you'll be entertained.
Paul Fairman wrote many short stories for popular magazines; one filmed as a Twilight Zone episode and another the basis for the films Invasion Of The Saucer Men (1957) and it's remake The Eye-Creatures (1967).
This harder to find paperback is available free online:
Project Gutenberg eBook > https://www.gutenberg.org/ebooks/20856
Librivox Audio by Karen Savage > https://librivox.org/ten-from-infinity-by-paul-w-fairman/
1963 / Paperback / 139 pages
thanks for sharing the gutenberg link, Eden. I have downloaded it. Seems interesting.