Example of Script.aculo.us method for AutoComplete. View HTML for code. Two other scriptaculous files required:
prototype.js
scriptaculous.js

Type some 911 incident in this box and then select suggested option from the list using the mouse or the up and down arrow keys. Once the selected word is in the box (by pressing enter), press your enter key again to input variable. You can do it all without the mouse too. Use arrow keys to select, press enter twice to submit.

Example, type in: oke

Input Variable: