Romancing the Stone

Joan Wilder (Kathleen Turner) is a lonely romance novelist in New York City, whom her editor believes is waiting for a romantic hero like in one of her books. One day Joan gets a call from her sister, Elaine, who has been kidnapped by antiquities smugglers, cousins Ira (Zack Norman) and Ralph (Danny DeVito). As Joan leaves her apartment to meet her editor, she is handed a letter containing a map, sent to her by late brother-in-law. Returning to her apartment, she finds it ransacked and the apartment supervisor dead. On the phone, Elaine tells Joan to go to Colombia with the map she received, it is Elaine's ransom.
Flying to Colombia, Joan is detoured from the rendezvous point by Colonel Zolo (Manuel Ojeda), the man who killed Elaine's husband. He tricks her into boarding the wrong bus, heading deep into the interior of the country instead of the coastal city of Cartagena, where Elaine is being held. When Joan asks the bus driver where they are going, she causes the bus to crash. As the rest of the passengers walk away, Joan is menaced by Zolo but is saved by American exotic bird smuggler Jack T. Colton (Michael Douglas), whose Jeep is wrecked in the bus crash. For getting her out of the jungle and to a telephone, Joan promises to pay Jack $375 in traveler's cheques.
Jack and Joan travel the jungle while eluding Zolo, who wants a treasure the map leads to and is chasing them with the military police. After spending a night hiding in a marijuana smuggler's crashed C-47 aircraft, they encounter a drug lord named Juan (Alfonso Arau), who is a big fan of Joan's novels and helps them escape from Zolo.
After a night of dancing and passion in town, Jack suggests to Joan that they find the treasure themselves before handing over the map. They follow the clues and locate an enormous emerald called El CorazÃ³n ("The Heart"). Unknown to Jack and Joan, they had used Ralph's car for the last leg of their journey while Ralph was sleeping in the back. Ralph takes the emerald from them at gunpoint. When Zolo appears, Jack steals the jewel back, but Jack and Joan are chased into a river and go over a waterfall. They end up on opposite sides of the raging river; Joan has the map, but Jack has the emerald. Jack directs Joan to Cartagena, promising that he will meet her there.
In Cartagena, Joan meets with Ira and Ralph who are still holding Elaine, but the exchange is interrupted by Zolo and his men, who have also captured Jack. Jack surrenders the emerald to Zolo, but a crocodile bites off Zolo's hand and swallows it along with the emerald. As a gun battle takes place between Zolo's soldiers and Ira's gang, Joan and Elaine dash for safety, pursued by Zolo. Jack tries to stop the crocodile from escaping but lets it go when he sees that Joan is in danger. Zolo charges at Joan, who eventually dodges his wild knife slashes, knocking Zolo into the crocodile pit. Ira and his men escape, but Ralph is left behind as the authorities arrive. After a kiss, Jack dives into the water after the crocodile, leaving Joan behind with her sister.
Some time later, Joan is back in New York City, delivering a new manuscript based on her adventure. Returning home, she finds Jack waiting for her in a sailboat named the Angelina, after the heroine of Joan's novels, and wearing boots made from the crocodile's skin. He sold the emerald and bought the boat of his dreams. They go off together, planning to sail around the world.

Question: Why does Jack let the crocidile escape?
Answer: Because he sees that Joan is in danger.