The Franklin Park Zoo is planning to build a glass-walled cage that allows visitors to again see the gorilla "Little Joe," who's been kept out of sight since he escaped three years ago and mauled a 2-year-old girl.

The new cage, featuring a mesh cap of woven steel to go with triple-layer glass walls, is part of $2.3 million renovation of the exhibition space inside the zoo's Tropical Forest building.

The renovation will allow visitors to view all seven of the zoo's gorillas, including Little Joe and another male, Okpara, who's aren't on display to prevent another escape.

"To get them back on exhibit will benefit our visitors and the gorillas — they enjoy being out there, and I'm sure (the gorillas are) looking forward to it with bated breath," said John Linehan, president of Zoo New England, the nonprofit entity that manages the zoo.

In September 2003, Joe leapt out of the exhibit in his second escape in two months. Joe reached the zoo pavilion, which he didn't get to on the first escape, and attacked 2-year-old Nia Scott and an off-duty zoo employee, Courtney Roberson, 18. They suffered cuts and bruises after Joe threw both to the ground and dragged them.

Joe was loose in the neighborhood for more than two hours before police subdued him with tranquilizer darts.

Roberson and Scott's mother sued the zoo and the cases are pending. On Friday, the lawyer representing both families told The Boston Globe that the zoo's improvements are too late.

"Why did it take two escapes and gorilla attacks on two innocent girls before Zoo New England finally decided to make the necessary modifications to the exhibit to contain this gorilla?" Donald Gibson asked.

Zoo officials said Joe, a juvenile, was an "extraordinary" animal whose weight hadn't caught up to the tremendous strength in his arms, enabling him to escape a cage surrounded by a 12-foot moat and electric-shock cables. They ruled out euthanizing Joe, a member of an endangered western lowland species, but couldn't risk putting him on display because they couldn't then afford a security upgrade.

Linehan said a test run of the enclosure, with the gorillas inside, will be conducted before it's opened to the public.

Until then, Joe and Okpara will continue their relatively quiet lives, as zookeepers keep them stimulated with new scents, gifts to unwrap and country and classical music selections. The male gorillas can also use an 80-foot-long outdoor run. The males and females are reunited every night, and Joe and Okpara are invariably happy to see the females, said Jeannine Jackle, assistant curator.

"They get very excited, and there's a lot of vocalizing and running around, a lot of chest-beating," she said.

Zoo visitor Lamarr Monterio, 24, of Easton said he's looking forward to Little Joe's return.

"It seems unfair that he's here but we can't see him," he said. "Gorillas — that's my favorite animal by far."