Four days after a alligator was spotted in the Humboldt Park lagoon, Frank Robb emailed Chicago Animal Care and Control and boldly said he could nab the reptile that had eluded searchers until that point. In two days.

But to do so, he wanted “to work in stealth,” “carry a knife” — and be paid $2,500, he wrote executive director Kelley Gandurski.

“This is not a guarantee but I am very confident in what I do,” he wrote. “I will bring my own equipment and gear and will catch the animal alive.”

As it turns out, it took Robb a little more than a day to catch the gator — and the animal was not harmed.

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Robb’s fee was one of the cheaper expenses from the weeklong hunt that drew hundreds of people or more to the park and captivated Chicago, documents released Wednesday show. In total, the search cost the city more than $33,000, including:

• $22,842 in labor and equipment costs for the Department of Streets and Sanitation to cordon off sections of the park;

• $6,140 in overtime pay for Animal Care and Control employees;

• and nearly than $1,200 for Robb’s travel and lodging.

Internal emails show that Robb came recommended by the staff at Brookfield Zoo after city workers and a local expert, known as Alligator Bob, failed to nab the reptile.

The day that Robb caught the gator, John Brueggen, the executive director of the St. Augustine Alligator Farm Zoological Park in Florida, reached out to Gandurski to offer to take the gator and pay for its flight out.

“We will be happy to take him into our collection,” Breuggen wrote. “Why shouldn’t he have an opportunity to retire in sunny Florida?”

Chicago police and the park district did not incur any extra costs during the search, the city said.