John Gill Commentary Exodus 21:16

"And he that stealeth a man, and selleth him, or if he be found in his hand, he shall surely be put to death." — Exodus 21:16 (ASV)

And he that stealeth a man, and selleth him
One of the children of Israel, as the Targums of Onkelos and Jonathan, and so the Septuagint version: but though this law was given to the Israelites primarily, yet was made for men stealers in general, as the apostle observes, who plainly has reference to it, (1 Timothy 1:9 1 Timothy 1:10) :

or if he be found in his hand ;
before the selling of him, as Jarchi notes, since he stole him in order to sell him, he was guilty of death, as follows:

he shall surely be put to death ;
with strangling, as the same Jewish writer remarks, as on the preceding verse; and Jarchi sets it down as a rule, that all death in the law, simply expressed, is strangling.