 Donald PleasenceDr. Hawley Harvey Crippen | Dr. Hawley Harvey Crippen |
 Coral BrowneBelle Crippen | Belle Crippen |
 Samantha EggarEthel Le Neve | Ethel Le Neve |
 Donald WolfitR.D. Muir (as Sir Donald Wolfit) | R.D. Muir (as Sir Donald Wolfit) |
 James Robertson JusticeCaptain McKenzie | Captain McKenzie |
 Geoffrey TooneMr. Tobin | Mr. Tobin |
| DDouglas Bradley-SmithDr. Pepper | Dr. Pepper |
 Olga LindoMrs. Clara Arditti | Mrs. Clara Arditti |
| EElspeth MarchMrs. Jackson | Mrs. Jackson |
 Paul CarpenterBruce Martin | Bruce Martin |
 John ArnattChief Inspector Dew | Chief Inspector Dew |
 Oliver JohnstonLord Chief Justice | Lord Chief Justice |
| JJohn LeeHarry | Harry |
 Edward UnderdownThe Governor | The Governor |
 Hamilton DyceDr. Rogers | Dr. Rogers |
 Basil HensonMr. Arditti | Mr. Arditti |
 Totti Truman TaylorMiss Curnow | Miss Curnow |
| EEdward CastHarding | Harding |
| CColin RixChemist | Chemist |
| TTerence BrookPolice Sergeant Outside Courtroom (uncredited) | Police Sergeant Outside Courtroom (uncredited) |
| EEric DodsonDefence QC Clerk (uncredited) | Defence QC Clerk (uncredited) |
 Max FaulknerRadio Officer Andrews (uncredited) | Radio Officer Andrews (uncredited) |
 Guy StandevenShips Steward (uncredited) | Ships Steward (uncredited) |
| JJohn TathamCourtroom Spectator (uncredited) | Courtroom Spectator (uncredited) |
