This answer format is too limited to give the entirety of steps by which Utterson detects Jekyll's lies but I can give you some highlights from which you can work. The first step, of course, came when Enfield, "his distant kinsman," pointed out the strange story connected with Jekyll's laboratory door as they passed by on a walk about town. Enfield told the story of a mysterious, monstrous and ruthless man who trampled over the fallen body of a young girl he had ruthlessly knocked down. This man took the assemblage of irate witnesses to Jekyll's laboratory door, which he opened with a key, and handed them a bank check drawn on the name of Dr. Jekyll to buy their placation and silence so the police would not be notified. Utterson heard the story because he knew the owner of the door, whereas Enfield did not.
Another step comes after Utterson contemplates the strange will stored in his safe in which Dr. Jekyll gives everything over to Mr. Hyde. Utterson tries to find information about Hyde from a mutual friend of Jekyll's, Dr. Lanyon, but he parted ways with Jekyll over the latter's unscientific research and knew nothing about Hyde. This drove Utterson to a very active step in discovering Jekyll's secret and detecting his lies.
Utterson was early and late, day after day, in Jekyll's neighborhood watching over the laboratory door to try to find Hyde:
In the morning before office hours, at noon when business was plenty, and time scarce, at night under the face of the fogged city moon, by all lights and at all hours ..., the lawyer was to be found on his chosen post.
"If he be Mr. Hyde," he had thought, "I shall be Mr. Seek."
One night, the long-ringing echo of the street foretold of Hyde's approach until he finally came into Utterson's view. After secretly watching what Hyde would do, Utterson stepped out to touch him on the arm and speak to him. The conversation was an odd and unpleasant one, with Hyde displaying his snarling laugh while claiming theirface-to-face meeting might prove useful. Utterson shuddered to think Jekyll might be so callous as to refer in this veiled way to Jekyll's will.
Mr. Utterson stepped out and touched him on the shoulder as he passed. "Mr. Hyde, I think?"
Mr. Hyde shrank back with a hissing intake of the breath. But his fear was only momentary; and though he did not look the lawyer in the face, he answered coolly enough: "That is my name. What do you want?"
The final step in detecting Jekyll's lies came when Utterson was beckoned by Poole to Jekyll's home as there was "something wrong." After breaking the interior laboratory door down because Utterson heard Hyde's voice instead of Jekyll's,
"Ah, that's not Jekyll's voice—it's Hyde's!" cried Utterson.
"Down with the door, Poole!"
Poole swung the axe over his shoulder; the blow shook the building, and the red baize door leaped against the lock and hinges.
they found a letter in which Jekyll made his full confession.