Accomplices and accessories are competent witnesses against the accused, and though a conviction may be had upon the uncorroborated testimony of such accessory or accomplice, the testimony should be received with great caution.2 A promise of immunity to an accomplice may be shown to impair the credibility of the witness, though it was not made by the prosecuting attorney, if it was made in his presence and the witness was a person of weak mind.3 But a conviction upon the uncorroborated evidence of a witness who admits that he has been promised immunity, insufficient to sustain a conviction.4

1 Hoagland vs. State, 17 Ind., 488; State vs. Laffer, 38 Iowa, 422; Harwell vs. State, 10 Lea (Tenn.), 544.

2 Cohn vs. People, 197 I11., 482; Kelly vs. People, 192 Ill., 119.