The spent cartridges found by the detective at the scene were identified as .38 caliber. The cartridges were a rimless cartridge that is much shorter than a .38 special casing which would be a rimmed cartridge. They appear to be .380 ACP which are used in a semi-automatic pistol. The aliens were using double action Colt revolvers fitted with silencers.
The police found 2 empty cartridges of .38 caliber from the fight with the Invaders at the beginning. The pistols used are revolvers, and revolvers only eject cartridges if the wielder ejects them. At no time during or after the fight were any cartridges ejected.
During the segment where David led the aliens into the radio transmitting station, the TV monitor was showing the security pictures in color even though it is an RCA Victor black and white TV. Also the security footage panned and came in for tighter views even though the cameras were in fixed positions securely mounted to the wall with no gimbals.