Pass this script an AWS access key ID and it will show you what IAM user has that key.

aws-access-key-to-iam-name.sh

#!/bin/bash -e
#
# Pass this script an AWS access key ID and it will show you what IAM user
# has that key.
#
# Usage:
# 	aws-access-key-to-iam-name some_key_id
#

readonly PROGNAME=$(basename $0)
readonly ARGS="$@"

check_command_exists() {
	type "$1" &> /dev/null ;
	if [ $? -eq 1 ]; then
		echo >&2 "$1 is required, you must install it before using this script."
	fi
}

get_all_iam_users() {
	aws iam list-users \
		| jq -r '.Users[] | ."UserName"' \
		> /tmp/aws_iam_users
}

get_all_access_key_ids() {
	echo 'Iterating through all AWS IAM users.'
	echo 'This may take a little while...'
	echo ''

	for user in `cat /tmp/aws_iam_users`
	do
		aws iam list-access-keys --user-name $user \
		>> /tmp/aws_access_key_ids.json
	done
}

find_and_show_access_key_owner() {
	cat /tmp/aws_access_key_ids.json \
		| grep -B 3 $ARGS \
		| sed -e 's/^[ \t]*//'
}

cleanup() {
	rm /tmp/aws_iam_users
	rm /tmp/aws_access_key_ids.json
}

usage() {
	cat <<- EOF
	usage: $PROGNAME options

	Finds the AWS IAM user that has a specific Access Key.
	
	OPTIONS:
		-h --help			show this help
		-x --debug			debug mode
	
	EXAMPLES:

	Run:
		$PROGNAME ABCDEFGHIJK123456789
	
	Output:
		"UserName": "my-iam-user",
		"Status": "Active",
		"CreateDate": "2014-06-26T13:44:04Z",
		"AccessKeyId": "ABCDEFGHIJK123456789"
	EOF
}

cmdline() {
	local arg=
	for arg
	do
		local delim=""
		case "$arg" in
			#translate --gnu-long-options to -g (short options)
			--help)           args="${args}-h ";;
			--debug)          args="${args}-x ";;
			#pass through anything else
			*) [[ "${arg:0:1}" == "-" ]] || delim="\""
				args="${args}${delim}${arg}${delim} ";;
		esac
	done

	#Reset the positional parameters to the short options
	eval set -- $args

	while getopts "hx:" OPTION
		do
			case $OPTION in
			h)
				usage
				exit 0
				;;
			x)
				readonly DEBUG='-x'
				set -x
				;;
			esac
		done

    return 0
}

main() {
	cmdline $ARGS

	# Check pre-requisites
	check_command_exists aws
	check_command_exists jq

	get_all_iam_users
	get_all_access_key_ids

	# Main function call that will show the IAM user associated with the
	# access key id passed as an arguement.
	find_and_show_access_key_owner

	# Get rid of cached lists when we're done.
	cleanup
}
main

Created fork that removes the jq dependency.
https://gist.github.com/mlehner616/7adedebce18e4c5388cf